This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. NMR The samples (30 mg) were deuterium-exchanged by lyophilization from D2O (99.9 % D), dissolved in 0.7 mL D2O, 10 [unreadable]L 50 mg/mL DSS in D2O (99.96 % D) was added, and the solution placed into a 5-mm NMR tube. One-dimensional proton NMR spectra were acquired on a Varian Inova-500 MHz instrument at 40 [unreadable]C. Spectral width was 5.5 kHz, transmitter frequency was set at -223 Hz, and 64 scans were collected in each experiment. The data were processed using the Mestre-C software using exponential multiplication (0.2 Hz). Spectra were referenced to the most upfield DSS signal (0.0 ppm). The spectra were baseline corrected with a third order Bernstein polynomial. The ratio of [unreadable]UA2S-H4 to [unreadable]UA-H4 was determined by integration of the signals at 5.97 ppm ( [unreadable]UA2S-H4) and 5.79 ppm ([unreadable]UA-H4).